This document records the generation of cost surfaces from mean frequency maps for the Liverpool Bay area. The cost rasters are generated using the new data obtained.
The purpose of this document is to record the process adopted to generate mean and most common rasters for use in the linkage between SWAT and Forel-Ule. The requirement is:
The plots show the frequency of the maximum Forel-Ule value, and water quality class (1-4; Citclops) for the period 2017-2020 for Jan to Dec.
These rasters give the mean FU class value for each cell per month over the period 2017-2021.
Here the FU classes rasters mean values are plotted. Here for plume 1.
And here as seasonal means (these are the mean value of ALL the rasters within that season in the period 2017 to 2021.
These rasters are saved.
Here the FU classes rasters mean values are plotted. Here for plume 2.
And here as seasonal means (these are the mean value of ALL the rasters within that season in the period 2017 to 2021.
These rasters are saved.
## Warning: package 'av' was built under R version 4.1.3
An empirical approach was taken to link the Forel-Ule class to the presence of DIN in the water. The water quality data uwas new data and was used to create a local polynomial regression fit between the Forel-Ule class and the concentration of nitrate, nitrite and ammonium in the water. To do so a fit was performed using the LOESS function for readings for “Nitrate and Nitrite” and for “Ammonium”. The polynomial fitting is shown in the figure below.
The cost functions were normalised to a 0.1-0.9 scale with 0.1 representing the highest exposure (in both cases class 21). To calculate the normalised function for DIN, the predicted concentrations for each Forel-Ule class was summed and then normalised against the summed values.
And here as a table of values:
| FUI | NormCost |
|---|---|
| 1 | 0.90 |
| 2 | 0.90 |
| 3 | 0.90 |
| 4 | 0.90 |
| 5 | 0.90 |
| 6 | 0.90 |
| 7 | 0.90 |
| 8 | 0.90 |
| 9 | 0.90 |
| 10 | 0.90 |
| 11 | 0.89 |
| 12 | 0.88 |
| 13 | 0.87 |
| 14 | 0.86 |
| 15 | 0.82 |
| 16 | 0.74 |
| 17 | 0.58 |
| 18 | 0.40 |
| 19 | 0.25 |
| 20 | 0.14 |
| 21 | 0.10 |
In this section we are using the normalised cost values that are 0.9 for the tertiary waters (FUI 1 to 9), and LOESS correlation prediction for a combination of Nitrate+Nitrite and Ammonium for FUI 10 to 21.
A plot of these cost surfaces is shown below: